Boiling is definitely my preferred method. It has always worked for me, in some cases with some pretty nasty water sources. I am not so sure that water literally has to reach the boiling point to kill bugs; after all, milk is pasteurized by heating to 165F which is the same temperature to which safely cooked meat should reach. Years ago, I routinely drank untreated water from mountain springs, but I am a bit more cautious now.